The present invention relates to an internal combustion engine system equipped with a supercharger and EGR in an intake air path.
There has been known a technology in which a supercharger driven by a motor is provided in an intake air path in order to increase the output of an internal combustion engine for the purpose of low fuel consumption of an automobile. There has been also known the mechanism of exhaust gas recirculation (hereinafter, referred to as “EGR”), which achieves a reduction in pumping loss or a reduction in nitrogen oxides (hereinafter, referred to as “NOx”) by recirculating a part of exhaust gas to the intake air side. As for a gasoline internal combustion engine, the EGR is placed; and accordingly, it becomes possible to open a throttle valve when the internal combustion engine is operated at low load and it becomes possible to improve fuel consumption of the internal combustion engine by reducing the pumping loss. As for the rest, like a lean burn engine, when the engine is operated with low fuel quantities, air becomes excess and thus combustion temperature rises to generate NOx. However, recirculation of exhaust gas is performed by the EGR; and accordingly, the combustion temperature can be lowered and the generation of NOx can be suppressed. Also, as for a diesel internal combustion engine, operation is performed by air mixed with exhaust gas to lower combustion temperature; and accordingly, a reduction in the generation of NOx can be achieved.
Incidentally, gas flowing in an EGR path flows from the higher side to the lower side in pressure distribution; and therefore, the pressure on the intake air side needs to be low in order to recirculate exhaust gas from the exhaust side to the intake air side. For this reason, for example, in a vehicle equipped with a turbocharger, a flow path on the exhaust side is taken out from the forward side of a turbine and a pressure drop of exhaust due to the presence of the turbine is utilized to recirculate exhaust gas to the intake air side. As for the rest, if a gasoline vehicle, there has been known a system that recirculates exhaust gas to the intake air side by utilizing that an intake manifold on the backward side of a throttle is negative pressure.
Under such a background, a supercharging system of an internal combustion engine disclosed in Japanese patent application No. 2001-509561A (U.S. Pat. No. 5,771,868) shows a configuration in which intake air of the EGR is recirculated to the upstream side of an electric supercharger and intake air (air sucked from the atmosphere) is mixed with exhaust gas to input to the electric supercharger. The exhaust gas is mixed with the intake air at a constant rate by this configuration; and accordingly, a reduction in NOx generated in the internal combustion engine is achieved.
Furthermore, a crankcase ventilation system disclosed in Japanese patent application No. 2003-206717A (U.S. Pat. No. 6,772,129 B2) shows an internal combustion engine equipped with a two step supercharging air amplification system. According to this configuration, recirculation gas by EGR is introduced to the upstream or the downstream of the electric supercharger depending on a driving state of a turbocharger and an electric supercharger. This enables exhaust gas to be recirculated on the basis of the pressure of each intake pipe; and therefore, the exhaust gas of the internal combustion engine can be purified.
Further, an EGR system of a vehicular internal combustion engine with a supercharger disclosed in Japanese patent application No. 2006-029273A includes an electric supercharger and a bypass valve that bypasses the electric supercharger; and an EGR path is placed between the electric supercharger and the bypass valve. According to this configuration, an operating range of introducing EGR is set to control the flow amount of exhaust gas recirculated from the EGR path depending on an operating state of the internal combustion engine. This improves responsiveness of the internal combustion engine during acceleration and accordingly exhaust emission can be improved.
The internal combustion engine needs to be mounted in a limited space in an automobile; and therefore, the internal combustion engine with good fuel consumption is required to be reduced in weight and in size as much as possible. Furthermore, an intake air flow path is preferable to be simple as much as possible in order to efficiently operate the internal combustion engine, because it becomes problematic that a complicated intake air flow path not only lowers the output of the internal combustion engine due to an intake air pressure drop but also increases in size due to an increase in the whole volume. However, in Japanese patent application No. 2001-509561A (U.S. Pat. No. 5,771,868) and Japanese patent application No. 2003-206717A (U.S. Pat. No. 6,772,129 B2), a problem exists in that the EGR path needs to be placed as far as near an inlet port of intake air and thus the length of an EGR path becomes long; and a problem exists in that it takes time until exhaust gas moves because the EGR path becomes long and thus controllability is deteriorated.
Furthermore, in Japanese patent application No. 2006-029273A), a problem exists in that, although the length of the EGR path is short, the bypass valve of the electric supercharger is needed and thus the configuration of the intake air path becomes complicated.